Electricity Cost Calculator
Calculate the operational cost and carbon footprint of running electrical appliances.
Appliance Presets
Operational Specs
Regional Rate Benchmarks
How utility operational costs are calculated
Operational electrical expense is derived from total energy consumption (measured in kilowatt-hours, kWh). The core equation is: kWh = (Power in Watts × Hours Used) / 1000. This consumption is multiplied by the utility tariff rate to determine the cost.
Carbon offsets are calculated using global grid carbon intensities (averaging ~0.475 kg CO2 emitted per kilowatt-hour of power produced).
Built and maintained by Meet Shah · Last updated
What this tool is used for
- Working out what leaving an appliance on actually costs per month.
- Comparing two appliances on running cost rather than purchase price.
- Checking whether replacing something old would pay for itself.
- Estimating the cost of a always-on device such as a router or a server.
- Working out a bill component from a meter reading.
How it works in practice
A worked example
A remote worker in Ohio runs a 1,500-watt space heater under the desk for six hours on each of the 22 workdays in a month and wants the cost before the bill arrives.
Appliance preset Electric Heater (1500W) Appliance Power 1500 W Currency Symbol USD ($) Rate per kWh 0.18 (from the bill) Hours per Day 6 Days per Month 22
OPERATIONAL COST DAILY COST $1.62 9.00 kWh MONTHLY COST $35.64 198.0 kWh YEARLY COST (12 × MONTHLY) $427.68 2376 kWh CARBON FOOTPRINT IMPACT Daily CO2: 4.27 kg (9.42 lbs) Monthly CO2: 94.0 kg (207.3 lbs) Yearly CO2 (12 × monthly): 1129 kg (2488 lbs) Based on global grid averages of 0.475 kg CO2 per kWh generated.
Every figure here is one quantity multiplied out. 1,500 watts is 1.5 kilowatts, six hours of it is 9 kilowatt-hours a day, and each row scales that by the rate and a count of days: the monthly row uses the 22 days typed in, so $35.64 is the price of a working month, and $1.62 is what one workday at the desk costs, the number to set against any fix that shortens the hours. The carbon rows apply one fixed factor, 0.475 kg of CO2 per kWh, to the same energy, which is why 198 kWh becomes 94 kg whichever grid the heater is actually plugged into.
The edge case that catches people
The yearly row is twelve of the monthly rows, and its label says so, which means it inherits Days per Month: this heater comes to $427.68 and 2,376 kWh a year, the cost of twelve working months. The field takes whole days, so a 30-day month makes a 360-day year, and for an appliance that never switches off, such as a fridge or a router, the yearly row runs about 1.4 per cent low; multiply the daily cost by 365 for that one. A seasonal load needs the opposite correction. A heater used only from November to March costs five of the monthly figure, not twelve.
When not to use this tool
Not for a carbon figure you intend to report. The CO2 rows multiply every kilowatt-hour by one global average, 0.475 kg, whatever currency or region is chosen, and real grids sit far from that in both directions: one running mostly on hydro or nuclear emits a small fraction of it, and a coal-heavy one more. Use your supplier's fuel-mix disclosure or your grid operator's published intensity instead. Treat the regional rate buttons the same way: they are fixed numbers built into the page, not live tariffs, and the currency menu only changes the symbol in front of the result; nothing is converted.
Frequently Asked Questions
- How is the cost calculated?
- Power in kilowatts × hours × the tariff rate. A 2 kW heater for three hours is 6 kWh, which at 30p is £1.80. The only conversion needed is watts to kilowatts, and forgetting it is a factor-of-a-thousand error.
- What is standby power actually costing?
- Less than it used to and more than nothing. Regulations pushed most devices below 0.5 W, but a household with fifty always-on devices still burns 20–50 W continuously — around 300 kWh a year, which is a real line on the bill for no benefit.
- Does a device draw its rated wattage constantly?
- Usually not. A rating is the maximum, and thermostatically controlled devices cycle — a fridge rated 150 W runs perhaps a third of the time. Using the nameplate figure as a continuous draw overstates the cost by a factor of two or three.
- What are time-of-use tariffs?
- Rates that vary by hour, sometimes dramatically. Where they apply, shifting a dishwasher or a car charge to an off-peak window changes the cost of the same energy substantially — which is why the tariff structure matters as much as the consumption.
- How do I find a device's real consumption?
- A plug-in energy monitor, which measures rather than estimates. It is the only way to capture duty cycle and standby together, and the results routinely contradict the nameplate — usually downward, occasionally alarmingly upward for older appliances.
Common errors and gotchas
- Using the unit rate without the standing charge, which on low usage dominates the bill.
- Confusing watts with kilowatt-hours, where one is a rate and the other a quantity.
- Using a nameplate rating as continuous draw, when most appliances cycle far below it.
- Ignoring a tariff's time-of-use bands, which can change the answer substantially.
- Forgetting VAT or sales tax, which the quoted rate may or may not include.